The septal region of the basal forebrain regulates information processing by hippocampal networks. Theta rhythm, the most prominent of hippocampal oscillations, facilitates synaptic plasticity and may influence memory processes. Lesions of the septal region or degeneration of septal cell populations impair theta rhythm generation and memory functions. Even though cholinergic septal neurons have been investigated, due to their early degeneration in Alzheimer's disease, other septal neuronal populations have remained incompletely characterized or uncharacterized. This proposal is aimed at anatomical identification and electrophysiological characterization of the septal neuronal populations that influence hippocampal theta rhythm generation. Because specific ionic conductance mechanisms play an important role in determining neuronal electrical properties and outputs, the characterization and investigation of their role in theta rhythm generation is an integral component of this proposal. The proposed experiments will advance our understanding of septal anatomy, physiology and septo-hippocampal function. They may also facilitate the discovery of molecular targets for pharmacological intervention aimed at alleviating the loss of cognitive functions observed in the elderly and in particular in Aizheimer's disease patients.